Light is light?

Ray, I appreciate your assertion that "light is light." But if that is so, then why all the rigamarole about micromoles and PAR meters and 'oh no, you can't trust your eye for the light your orchids are receiving from LEDs.' (I have yet to read a comment on the fact that PAR and human sensitivity to light are roughly equivalent). Diversionary tactics? For practical purposes, different sources of light behave differently. Isn't that all we're interested in? Those of us who are scrambling for a light source to replace the sunlight that we don't have? How a given source of light behaves? HID opposed to fluorescent, as opposed to LED? Isn't this what everyone is trying to figure out? And there are real, practical differences. Depending on the fashion, everyone touts the drawbacks of one and the strong points of the other. But who is saying, impassionately, what each ones does, and doesn't do? Why, at this point, isn't there a "Bible" for growing under artificial light? Maybe there is and I've just missed it.

So, what I've noticed, given my reasonably competent on-the-fly setup, is the spike on my Phal. schilleriana. There is a huge amount of difference between the buds on the lower part of the spike and the upper part of the spike, and it's a short spike - the first to bloom on this plant. It all fits under my light set-up. The spike will not elongate at the terminus because the nature of schilleriana is that buds develop and bloom simultaneously. I could be wrong, but I don't think this would have happened with HID light, whatever one might say about wasted energy in heat. I appreciate the learning that can compute light fall-off, but the thing about HID light is that there is more flexibility as to placement and natural blooming. With LEDs, this doesn't seem to be the case. Why is that? Oh, I think I just answered my own question. You'll forgive the process I have to go through. And maybe you will even confirm it. With HID, there is more energy that evens out light "scattering." So, the range of useful light is widened and more generalized (and would yield a more natural blooming on tall spikes, for example). With LEDs, the angle of useful light is more focused and the energy is reduced to produce that more narrow angle of useful light, but in which the intensity escalates or de-escalates rapidly. So it would be difficult if not impossible to replicate the generalized coverage of HID light with LED light because the focus of LED light is comparatively narrow. I don't know. Am I on the right track? If so, some "wasted" heat energy would seem worthwhile for more natural blooming. Assuming it is affordable for a given grower.

PAR refers to the photosynthetically active photons between 400 & 700 nm wavelength. Micromoles per square meter per second is simply the rate at which those photons are hitting the plants. PPFD - photosynthetic photon flux density. Those terms apply to all light sources when applying them to horticulture. A given plant needs "so many" photons in that PAR range over the course of a day. Period. End of paragraph. (By the way, you should use them more; that big post was awfully difficult to read...)

If PPFD were given for every light source and we knew the needs of each type of plant, all would be well when deciding from different light sources and we'd never have these discussions!

No, the human eye and plants don't "see" light the same. Yes, both DO see everything in the PAR spectrum, but it's the sensitivity across that range that is different. The human eye is particularly sensitive to the middle of the spectrum, while chlorophyll is less sensitive there and more sensitive at the ends - which is why red & blue LEDs work for plants.

The PAR concept bothers me a bit, as it implies that as long as the photons are in that range, all is well. Within limits that's true, but a plant grown under the same number of photons of 100% 400 nm light and one grown under 100% 700 nm light absolutely will NOT grow the same! Fortunately, most "white" light sources have a broad enough spectral range that the plants are "photonically satisfied" by the spectrum, making the PPFD the important part, and the difference between light sources. Certainly there are gross spectral differences - sodium vapor being mostly in the red end, metal halide mostly in the blue, etc., but there is "enough" in the rest of the spectrum to grow things satisfactorily.

The photons coming from a light source behave the same. Let's say we have a MH bulb and a LED that each put out 100 micromoles per second in the PAR wavelengths. Again, the LED will project (at most) over 180 degrees (chip on board) versus 360 for the HID tube, making the LED more focused and efficient, but in both cases the photons spread out, decreasing in density per the inverse square of the distance.

Your second long paragraph basically supports that and the rest of my configuration comments.

Yes, I should have organized the post better. It was an undisciplined and self-gratifying stream of conscious piece. Apologies and thanks for making the effort to parse it out and reinforce my path through LED land. It seems true, what they say, that whenever your orchid setup substantially changes, you have to learn how to grow all over again. It's taxing my patience. All things considered, I love LEDs, and mine in particular. I can live with them and my orchids in the same room, they don't hum, if they dominate the room, it's in a reasonably aesthetic way, and my plants are growing. The way my bulbs focus the light, which I complained about, makes it less generally bothersome to me.

I think this whole subject area is fascinating - but too undefined (or un-datafied) at this point. For quite a while I participated in a LinkedIn group that was designing and building computer-controlled LED panels so that experiments could be conducted to define exactly what specific wavelengths did to plant growth. One of the more fascinating aspects for me was the fact that bell pepper plants, when exposed for a couple of hours to a specific wavelength, "reset" their internal clocks and went back to fruit production, even though unexposed plants just gradually died after that process.

As far as the "stream of consciousness" is concerned, I suffer from that as well. I publish a monthly newsletter, and bought dictation software to ease that process, but sometimes my culture articles end of being HUGE, so I have to go back and prune them accordingly.

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